In many airplanes, cargo is loaded not only through the nose section of the airplane but through a side cargo door as well. In order to keep loaded cargo inside the airplane until it can be secured to the main cargo deck, it is common practice to employ stop assemblies near the sill of the side cargo door. In essence, the stop assemblies are one-way gate assemblies that allow cargo to pass in the inboard direction but obstruct passage in the outboard direction after the cargo has cleared the stop assembly.
Current stop assemblies consist of a contacting surface, usually a plate, connected through a complex linkage to a separate stop having an abutment surface. When such stop assemblies are in their normal nonengaged status, both the contacting surface and the separate stop are in upright positions. As cargo is rolled over the stop assembly in an outboard to inboard direction, the leading edge of the cargo engages the contacting surface, which begins to collapse to a position below the bottom of the cargo. Acting through the complex linkage, collapse of the contacting surface also causes collapse of the stop. Such stop assemblies are spring loaded, so that after the cargo has passed to a position inboard of the stop assembly, the contacting surface and the stop return to their normal upright positions. The abutment surface of the stop then acts to prevent backward outboard movement of the cargo.
Because of the great number, and sophistication, of the parts used in the complex linkage of current stop assemblies, they are expensive to produce. Due to the intricacy of the parts in the complex linkage, it is common for the linkage to break after a period of sustained impact to the abutment surface by airline cargo containers and pallets. Repair of such linkage is also quite expensive.
Another problem incident to current stop assemblies is that the stop containing the abutment surface may be inadvertently knocked down after the cargo has passed the stop assembly to an inboard position. This occurs because it is common for cargo containers and pallets to warp upwardly about their periphery after extended use. Because the contacting surface of current stop assemblies has a higher elevation than the stop containing the abutment surface, when warped containers and pallets move in an outboard direction, as they may do on occasion, their upwardly warped leading edge can pass above the abutment surface of the stop and engage the contacting surface. This causes the stop to collapse and allow free outboard movement of the container or pallet, thereby eliminating the entire function of the stop assembly.
Yet another problem incident to current stop assemblies is that they are easily stolen due to the quick-release manner in which they are attached to the main cargo deck of the airplane. This is a particular problem in some of the less secure airports in underdeveloped countries of the world. Given the expensive nature of current stop assemblies, and their nearly uniform use throughout the industry, black markets for such stop assemblies have developed in various pockets of the world.
As a result of the reasons detailed above, there has been a long-felt need for a stop mechanism applicable to the side loading door of cargo airplanes that is relatively inexpensive to produce, that has an abutment surface and general design capable of withstanding sustained impact loads, that circumvents the warped container and pallet problem, and that attaches to existing fittings in a manner that reduces the possibility of theft. This invention is directed to satisfying this need.